This invention relates to current transformers and in particular, it relates to variable gain electronic current transformers.
In the measurement of electrical energy, such as that flowing into homes and industrial developments, numerous efforts have been made to provide reliable and efficient, yet economical means for measuring and recording the electrical energy consumed. Examples of recent developments in the electrical energy measuring technology are disclosed in the patent applications of Miran Milkovic, Ser. No. 361,030 , filed May 17, 1973 , now U.S. Pat. No. 3,875,509 , issued Apr. 1, 1975 , and Ser. No. 395,142 , filed Sept. 7, 1973 , now U.S. Pat. No. 3,875,508, issued Apr. 1, 1975, wherein solid state electronic meters are disclosed for measuring the flow of energy in a power system. These applications disclose a method and apparatus for detecting the current flow through at least one line and the voltage of a line which parameters are appropriately multiplied and converted to a pulse train signal which is counted in a display mechanism to provide an indication of the electrical energy being consumed. These solid state electrical energy meters, however, have a critical drawback in that the dynamic range thereof is somewhat limited and the signal-to-offset or the signal-to-noise ratio must be improved in order to provide a more accurate meter for measuring a wide range of power flow past a given point. Accurate sensing of AC currents by using conventional current transformers has not been simple because of the relatively large current dynamic range experienced in both industrial and residential power systems. Thus, present-day current transformers capable of transforming AC currents over a rather large dynamic range are both expensive and large and accordingly, have proven to be quite uneconomical. It therefore has become desirable to provide a simple, economical variable current transformer which can be packaged in a relatively small container for transforming AC currents over a substantial dynamic range.
It therefore is an object of the present invention to provide a variable gain electronic current transformer for transforming AC currents over a large dynamic range.